In ordinary rooms or in clean rooms, such as bio clean rooms, airborne particles, including microorganisms, are detected and recorded using particle detecting devices. See, for example, U.S. Pat. No. 5,701,012, Japanese Unexamined Patent Application Publication Nos. 2008-225539 and 2011-083214, and N. Hasegawa, et al., Instantaneous Bioaerosol Detection Technology and Its Application, azbil Technical Review, 2-7, Yamatake Corporation, December 2009.
The optical particle detecting device comprises, for example, a chamber, an injection nozzle that is provided in the chamber, and a discharge nozzle that is provided in the chamber facing the injection nozzle. The particle detecting device draws in, for example, a fluid, such as air, within the room wherein the particle detecting device is placed, and sprays it, as a sample fluid, from the injection nozzle into the chamber. Additionally, the fluid within the chamber is discharged to the outside of the particle detecting device through the discharge nozzle. Furthermore, the particle detection device is provided with a detecting mechanism for illuminating, with a light beam, the sample fluid that is sprayed from the injection nozzle to detect particles included within the sample fluid. When there is a particle included within the sample fluid, a particle that is illuminated with light emits fluorescence or produces scattered light, enabling detection of the numbers, sizes, and the like, of particles included in the sample fluid.
Here, in the injection nozzle of the chamber, the cross-sectional area of the sample fluid that is introduced from the outside is constricted, increasing the speed of the flow, thus decreasing the surrounding pressure. Because of this, opposing flows are produced around the flow of the sample fluid that is formed between the injection nozzle and the discharge nozzle. Furthermore, there are cases wherein the discharge of the fluid from the discharge nozzle does not go smoothly because of the drop in pressure within the chamber. When opposing flows are produced within the chamber or when there is a pressure drop within the chamber, particles may remain stagnant within the chamber. When particles remain stagnant within the chamber, then the detecting mechanism may count the same particle multiple times, which may make it difficult to detect accurately the number of particles included in a unit volume of the fluid.
In this regard, a method has been proposed wherein the interior of the chamber is pressurized through supplying a pressurizing fluid, from which particles have been eliminated, into the chamber from an opening other than the injection nozzle. See, for example, U.S. Patent Application Publication No. 2013/0248693.
However, the present inventor discovered that there may be cases wherein the flow of the pressurizing fluid, injected from an opening other than the injection nozzle, may disrupt the flow of the sample fluid between the injection nozzle and the discharge nozzle. When the flow of the sample fluid between the injection nozzle and the discharge nozzle is disrupted, the particles included in the sample fluid that should be discharged from the discharge nozzle may remain stagnant within the chamber. If particles that remain stagnant within the chamber are detected multiple times, then there may be an incorrect evaluation of the number of particles included within the sample fluid. Moreover, the particles that remain stagnant within the chamber may cause contamination. Given this, an aspect of the present invention is to provide a particle detecting device wherein there is less of a tendency for particles to remain stagnant internally.